Efficient Homogeneous Hydridoirida-β-Diketone-Catalyzed Methanolysis of Ammonia-Borane for Hydrogen Release in Air. Mechanistic Insights

The hydridoirida-beta-diketone [(IrH{(PPh2(o-C6H4CO))(2)H})(2)(mu-Cl)][BF4] (2) has been used as a homogeneous catalyst for the methanolysis of ammonia-borane to release up to 3 equivalents of hydrogen in the presence of air. With catalyst loadings as low as 0.2 mol%, ammonia-borane undergoes methanolysis within 6 min at 30 degrees C, with TOF50% of 320 mol(H2) .mol(Ir)(-1).min(-1), or within 80 s at 60 degrees C, with an excellent TOF50% of 1991 mol(H2).mol(Ir)(-1).min(-1), and maintains its catalytic activity in consecutive runs. Triethylamine-borane fails to undergo methanolysis. Kinetic studies indicate first-order dependence on substrate and on catalyst concentration and suggest cleavage of the solvent O-H bond being involved in the rate determining step of the reaction. In methanol solution 2 forms cationic [IrH(MeOH){(PPh2(o-C6H4CO))(2)H}](+) (3) and reacts with Me3N-BH3 to afford a hydridoirida-beta-diketone [IrH(Me3NBH3){(PPh2(o-C6H4CO))(2)H}](+) (4), with the borane adduct eta(1)-coordinated to iridium. Compound [4][BAr4F] shows dynamic behaviour in solution due to exchange of bridging and terminal B-H bonds. A multinuclear NMR study of the catalyzed reaction shows the formation of two ammonia-methoxyborane adduct intermediates, H3N-BH2(OCH3) and H3N-BH(OCH3)(2), and an iridium species proposed of the hydridodiacyl type [IrH(H3NBH3-x(OCH3)(x))(PPh2(o-C6H4CO))(2)] with a coordinated borane adduct. On account of experimental evidence, a simplified catalytic cycle is suggested for the methanolysis of AB to release hydrogen.Partial financial support by Ministerio de Economia y Competitividad MINECO/FEDER (CTQ2015-65268-C2-1-P and PID2019-111281GB-I00), Gobierno Vasco (GIC 18/143 and IT1180-19) Universidad del Pais Vasco (UPV/EHU) and Diputacion Foral de Gipuzkoa are gratefully acknowledged. I. B. acknowledges support by UPV/EHU

Formation of Irida-β-ketoimines and PCNamine-Ir(III) Complexes by Reacting Irida-β-diketones with Aliphatic Diamines: Catalytic Activity in Hydrogen Release by Methanolysis of H3N–BH3

Aliphatic diamines [(H2N(CH2)nNHR) (a–d) n = 2: R = H (a), R = CH3 (b), R = C2H5 (c), n = 3, R = H (d) or rac-2-(aminomethyl)piperidine (e)] react with [IrH(Cl){(PPh2(o-C6H4CO))2H}] in THF to afford ketoimine complexes [IrH(Cl){(PPh2(o-C6H4CO))(PPh2(o-C6H4CN(CH2)nNHR))H}] (2a–2d) or [IrH(Cl){(PPh2(o-C6H4CO))(PPh2(o-C6H4CNCH2(C5H9NH)))H}] (2e), containing a bridging N–H···O hydrogen bond and a dangling amine. Complex 2e consists of an almost equimolar mixture of two diastereomers. In protic solvents, the dangling amine in complexes 2 displaces chloride to afford cationic acyl-iminium compounds, [IrH(PPh2(o-C6H4CO))(PPh2(o-C6H4CNH(CH2)nNHR))]X (3a–3d, X = Cl) or [IrH(PPh2(o-C6H4CO))(PPh2(o-C6H4CNHCH2(C5H9NH)))]Cl (3e) and (4a–4b, X = ClO4), with new hemilabile terdentate PCNamine ligands adopting a facial disposition. Complexes 3 contain the corresponding phosphorus atom trans to hydride and the amine fragment trans to acyl, while complexes 4 contain the amine trans to hydride. 3b and 4b consist of 80:20 and 95:5 mixtures of diastereomers, respectively, while 3e contains a 65:35 mixture. In the presence of KOH, intermediate cationic acyl-iminium complexes 3 transform into neutral acyl-imine [IrH(PPh2(o-C6H4CO))(PPh2(o-C6H4CN(CH2)nNHR))] derivatives (5) with retention of the stereochemistry. Single-crystal X-ray diffraction analysis was performed on 2a, [3a]Cl, [3b]Cl, [4a]ClO4, and 5b. Complexes 2, 3, and 5 catalyze the methanolysis of ammonia-borane under air to release hydrogen. The highest activity is observed for ketoimine complexes 2.Partial financial support by Ministerio de Economía y Competitividad MINECO/FEDER (CTQ2015-65268-C2-1-P and PID2019- 111281GB-I00), Gobierno Vasco (GIC 18/143 and IT1180-19) Universidad del País Vasco (UPV/EHU), and Diputación Foral de Gipuzkoa are gratefully acknowledged. I. B. acknowledges support by UPV/EHU

A Lamellar Zn-Based Coordination Polymer Showing Increasing Photoluminescence upon Dehydration

The present study reports on a 2D lamellar coordination polymer (CP) of {[Zn(µ3-pmdc)(H2O)]·H2O}n formula (pmdc = pyrimidine-4,6-dicarboxylate). This CP is synthesized under an appropriate acid-base reaction between the gently mortared reagents in the solid state through a solvent-free procedure that avoids the presence of concomitant byproducts. The X-ray crystal structure reveals the occurrence of Zn2 entities connected through carboxylate groups of pmdc, which behave as triconnected nodes, giving rise to six-membered ring-based layers that are piled up through hydrogen bonding interactions. In addition to a routine physico-chemical characterization, the thermal evolution of the compound has been studied by combining thermogravimetric and thermodiffractometric data. The photoluminescence properties are characterized in the solid state and the processes governing the spectra are described using time-dependent density-functional theory (TD-DFT) with two different approaches employing different program packages. The emissive capacity of the material is further analyzed according to the dehydration and decreasing temperature of the polycrystalline sampleThis research was funded by Gobierno Vasco/Eusko Jaurlaritza (IT1755-22, IT1722-22 and IT1500-22) and Junta de Andalucía (B-FQM-734-UGR20, ProyExcel_00386 and FQM-394)

Irida-β-ketoimines derived from Hydrazines to Afford Metallapyrazoles or N-N Bond Cleavage: A Missing Metallacycle Disclosed by a Theoretical and Experimental Study

Unprecedented metallapyrazoles [IrH2{Ph2P(o-C6H4)CNNHC(o-C6H4)PPh2}] (3) and [IrHCl{Ph2P(o-C6H4)CNNHC(o-C6H4)PPh2}] (4) were obtained by the reaction of the irida-β-ketoimine [IrHCl{(PPh2(o-C6H4CO))(PPh2(o-C6H4CNNH2))H}] (2) in MeOH heated at reflux in the presence and absence of KOH, respectively. In solution, iridapyrazole 3 undergoes a dynamic process due to prototropic tautomerism with an experimental barrier for the exchange of ΔGcoal⧧ = 53.7 kJ mol–1. DFT calculations agreed with an intrapyrazole proton transfer process assisted by two water molecules (ΔG = 63.1 kJ mol–1). An X-ray diffraction study on 4 indicated electron delocalization in the iridapyrazole ring. The reaction of the irida-β-diketone [IrHCl{(PPh2(o-C6H4CO))2H}] (1) with H2NNRR′ in aprotic solvents gave irida-β-ketoimines [IrHCl{(PPh2(o-C6H4CO))(PPh2(o-C6H4CNNRR′))H}] (R = R′ = Me (5); R = H, R′ = Ph (8)), which can undergo N–N bond cleavage to afford the acyl–amide complex [IrHCl(PPh2(o-C6H4CO))(PPh2(o-C6H4C(O)N(CH3)2))-κP,κO] (6) or [IrHCl(PPh2(o-C6H4CO))(PPh2(o-C6H4CN)-κP)(NH2NHPh-κNH2)] (9) containing o-(diphenylphosphine)benzonitrile and phenylhydrazine, respectively. From a CH2Cl2/CH3OH solution of 9 kept at −18 °C, single crystals of [IrHCl(PPh2(o-C6H4CO))(PPh2(o-C6H4CN)-κP))(HN═NPh-κNH)] (10) containing o-(diphenylphosphine)benzonitrile and phenyldiazene were formed, as shown by X-ray diffraction. The reaction of 1 with methylhydrazine in methanol gave the hydrazine complex [IrCl(PPh2(o-C6H4CO))2(NH2NH(CH3)-κNH2)] (7). Single-crystal X-ray diffraction analysis was performed on 6 and 7.Partial financial support by Ministerio de Economía y Competitividad (CTQ2015-65268-C2-1-P and CTQ2015-65268-C2-2-P), Gobierno Vasco (S-PE13UN023), and Universidad del País Vasco (UPV/EHU) (GIU 13/06) is gratefully acknowledged. I.Z. is grateful to Gobierno Vasco for a scholarship. Technical and human support provided by IZO-SGI, SGIker (UPV/EHU, MICINN, GV/EJ, ERDF, and ESF) is gratefully acknowledged

Synthesis of nickel-thiolate complexes

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Structure of a dinickel(II)-dithiolate bridged macrocyclic complex synthesised via a novel solvent-assisted disulfide cleavage reaction

The reaction of 2,6-diformyl-4-methylphenyl disulfide with [Ni(tn)3]Cl2 (tn = 1,3-diaminopropane), in methanol and in the presence of NaBPh4 resulted in the isolation of [Ni2(L1)](DMF)2(BPh4)2 (I), (L1 = 15,95-dimethyl-3,7,11,15-tetraaza-1,9(1,3)-dibenzenacyclohexadecaphane-2,7,10,15-tetraene-12,92-bis(thiolate). This reaction represents a 2-electron solvent assisted reduction of the disulfide bond to form two thiolate ligands where methanol is converted to formaldehyde and the two nickel centres remained in the + 2 oxidation state. The crystal structure of I showed the two nickel(II) atoms are bridged by two thiolates in a binuclear Ni2S2 core inside of a macrocyclic framework. The IR spectrum showed a band at 1625 cm−1, assigned to the imine ν(C [dbnd]N) stretch of the macrocyclic ligand, and bands at 734, 706 cm−1, are assigned to the tetraphenylborate counter ions. This is the first example of solvent assisted S–S bond cleavage being used to prepare a dicompartmental macrocyclic complex.</p

Synthesis and structures of mono and binuclear nickel(II) thiolate complexes of a dicompartmental pseudo-macrocycle with N(imine)2S2 and N(oxime)2S2 metal-binding sites

The reaction of [Ni(pftp)] [pftp = N,N-propane-1,3-diyl-(6-formyl-4-methyliminatothiophenolato)] with hydroxylamine hydrochloride in the presence potassium acetate in MeOH resulted in the formation of the complex [Ni(LH2)] [L = N,N-propane-1,3-diyl-(4-methyl-2-methyliminato-6-methyloxime-thiophenolato)] in good yield. A single crystal X-ray diffraction structural determination showed a mononuclear nickel(II) complex with the new acyclic ligand LH2 that had been functionalised with two oxime groups containing an empty N(oxime)2S2 pocket to which another metal ion could be added. A further reaction of [Ni(LH2)] with NiCl2·6H2O, triethylamine and ammonium hexafluorophosphate in MeOH gave a dark red product that yielded red crystals of [Ni2(LH)]PF6·DMF via slow recrystallisation from a DMF/PriOH solvent mixture. A single crystal X-ray diffraction study of these crystals confirmed the presence of a dinuclear nickel(II) complex linked by a dithiolato-bridge. Both nickel(II) ions exhibited square-planar geometry where the metal centres are coordinated in two distinct cis-S2N(imine)2 and cis-S2N(oxime)2 binding sites provided by the new dicompartmental oxime/thiolate-containing ligand L